How would you describe the lava in a lava lamp?

How about the adjective amorphous? Lacking a defined shape, or having a shape that shifts.

I'm partial to "transmogrify", or it's heftier noun version, "transmogrification" - meaning "to change or alter greatly and often with grotesque or humorous effect" - per MW-O

What astonished me was how old this word is:

Origin of TRANSMOGRIFY (MW-O):

origin unknown

First Known Use: 1656

In a lava lamp, the floating luminous waxy substance is called a blob. (Another similar word is a glob, a colloquial word derived from globule). Blob can also be used as a verb and blobbing can be used as a participial adjective derived from the verb blob (or can be used as a present participle verb).

The noun definition of blob from OED:

A drop or globule of liquid or viscid substance. Also figurative.

The related verb definitions of blob from OED:

intransitive. To rise in a bubble or bubbles.

intransitive ? To produce blobs or bubbles; to ‘flop’ in the water.

Here is an example with the noun blob:

The lava lamp glooped its way into pop culture history with its ascending and descending blobs of wax. - gizmodo.com

Here is an example with the adjective blobbing:

On a table beside a blobbing orange lava lamp were framed photos.

_{Life Support - By Candace Calvert}